passes/pmgen/peepopt_shiftmul.pmg

pattern shiftmul
//
// Optimize mul+shift pairs that result from expressions such as foo[s*W+:W]
//

state <SigSpec> shamt

match shift
	select shift->type.in($shift, $shiftx, $shr)
endmatch

code shamt
	shamt = port(shift, \B);
	if (shamt.empty())
		reject;
	if (shamt[GetSize(shamt)-1] == State::S0) {
		do {
			shamt.remove(GetSize(shamt)-1);
			if (shamt.empty())
				reject;
		} while (shamt[GetSize(shamt)-1] == State::S0);
	} else
	if (shift->type.in($shift, $shiftx) && param(shift, \B_SIGNED).as_bool()) {
		reject;
	}
	if (GetSize(shamt) > 20)
		reject;
endcode

match mul
	select mul->type.in($mul)
	select port(mul, \A).is_fully_const() || port(mul, \B).is_fully_const()
	index <SigSpec> port(mul, \Y) === shamt
endmatch

code
{
	IdString const_factor_port = port(mul, \A).is_fully_const() ? \A : \B;
	IdString const_factor_signed = const_factor_port == \A ? \A_SIGNED : \B_SIGNED;
	Const const_factor_cnst = port(mul, const_factor_port).as_const();
	int const_factor = const_factor_cnst.as_int();

	if (GetSize(const_factor_cnst) == 0)
		reject;

	if (const_factor_cnst.bits[GetSize(const_factor_cnst)-1] != State::S0 &&
			param(mul, const_factor_signed).as_bool())
		reject;

	if (GetSize(const_factor_cnst) > 20)
		reject;

	if (GetSize(port(shift, \Y)) > const_factor)
		reject;

	int factor_bits = ceil_log2(const_factor);
	SigSpec mul_din = port(mul, const_factor_port == \A ? \B : \A);

	if (GetSize(shamt) < factor_bits+GetSize(mul_din))
		reject;

	did_something = true;
	log("shiftmul pattern in %s: shift=%s, mul=%s\n", log_id(module), log_id(shift), log_id(mul));

	int new_const_factor = 1 << factor_bits;
	SigSpec padding(State::Sx, new_const_factor-const_factor);
	SigSpec old_a = port(shift, \A), new_a;
	int trunc = 0;

	if (GetSize(old_a) % const_factor != 0) {
		trunc = const_factor - GetSize(old_a) % const_factor;
		old_a.append(SigSpec(State::Sx, trunc));
	}

	for (int i = 0; i*const_factor < GetSize(old_a); i++) {
		SigSpec slice = old_a.extract(i*const_factor, const_factor);
		new_a.append(slice);
		new_a.append(padding);
	}

	if (trunc > 0)
		new_a.remove(GetSize(new_a)-trunc, trunc);

	SigSpec new_b = {mul_din, SigSpec(State::S0, factor_bits)};
	if (param(shift, \B_SIGNED).as_bool())
		new_b.append(State::S0);

	shift->setPort(\A, new_a);
	shift->setParam(\A_WIDTH, GetSize(new_a));
	shift->setPort(\B, new_b);
	shift->setParam(\B_WIDTH, GetSize(new_b));

	blacklist(shift);
	accept;
}
endcode